The present invention relates to a magnetic suspending device for magnetically suspending a magnetizable controlled object without contact at an arbitrary position by making use of magnetic attractive or repulsive forces generated by electromagnets.
FIG. 1 is a schematic diagram showing the construction of a magnetic suspending device of this type, and FIG. 2 is a circuit diagram showing the construction of a control device for controlling the magnetic suspension and support of the magnetic suspending device. As shown in those figures, the magnetic suspending device comprises a pair of electromagnets 11, 13 disposed opposite to each other, a magnetizable controlled object 15 disposed between the pair of electromagnets and position displacement detection sensors 12, 14 disposed opposite to each other for detecting a position displacement of the controlled object 15.
Detection signals from the position displacement detection sensors 12, 14 are inputted into a control circuit unit 20 for performing phase compensation and gain adjustment, and magnetic attractive or repulsive forces generated by the pair of electromagnets 11, 13 are controlled by control outputs from the control circuit unit 20 so as to suspend the controlled object 15 without contact at an arbitrary position between the pair of electromagnets 11, 13.
The control circuit unit 20 comprises load resistors 21, 22, a sensor signal processing circuit unit 23, an offset adjusting circuit unit 24, a phase compensating circuit unit 25, a gain adjusting circuit unit 26, a main amplifier unit 27 and a threshold outputting unit 28. Detection signals from the position displacement detection sensors 12, 14 are directed to the phase compensating circuit unit 25 and the gain adjusting circuit unit 26 for phase compensation and gain adjustment through the load resistors 21, 22, the sensor signal processing circuit unit 23 and the offset adjusting circuit unit 24, and the signals so compensated and adjusted are then fed back to the electromagnets 11, 13 through the main amplifier unit 27.
Examples of such a control circuit unit are described in Japanese Patent Publication No. Sho 61-37643 and Japanese Patent Laid-open No. Hei 9-257035, and those documents are expressly incorporated herein by reference in its entirety.
In a magnetic suspending device utilizing such a closed-loop control as described above, the controlled object 15 magnetically suspended by magnetic attractive or repulsive forces generated by the pair of electromagnets 11, 13 receives strong electromagnetic forces from the electromagnets 11, 13 or rotational driving electromagnets (not shown) at any time while being magnetically suspended. This generates secondary current flows in the controlled object 15 in such a direction as to cancel the electromagnetic forces received from the electromagnets 11, 13, and this secondary current flows and the electrical resistance of the controlled object 15 itself generate secondary loss heat.
The above described magnetic suspending device is used, for example, as a magnetic bearing device. in this case, it is difficult to dissipate heat from the controlled object 15 and/or cool the object 15 by virtue of heat conduction, because the construction of the magnetic suspending device allows the secondary loss heat, generated in the controlled object 15, to be generated only in a state in which the controlled object 15 is held without contact. In particular, in the case of a magnetic bearing device used in a vacuum atmosphere, since there exists very little heat conductive substance such as gas between the controlled object 15 and the electromagnets 11, 13 surrounding the object, the controlled object 15 can be cooled only to a very small extent by virtue of heat conduction. Therefore, if the controlled object 15 is heated abnormally by being run for a long time or by radiation heat received from the surrounding environment of the magnetic bearing device, it is difficult to dissipate heat to the outside of the device.
As described above, in a case where the temperature of the controlled object 15 goes up abnormally, it will cause materials (such as metal) deformation and/or brittle fracture of respective constituent components of the controlled object 15, resulting in a failure fatal to the device.
With a view to preventing such a failure, a protective means has been developed in which the magnetic suspending device is operated, by measuring and monitoring the temperature of the controlled object 15, within a range of temperature where the respective constituent components of the controlled object 15 can safely be used. Conventionally, such a protective means has been used to measure the temperature of the controlled object by means of an optical means such as a radiation thermometer so as to stop the operation of the control device of the magnetic suspending device when a measured temperature becomes equal to or higher than a predetermined temperature.
As described above, when the temperature of the controlled object 15 is measured by a radiation thermometer, the temperature needs to be measured directly by detecting infrared radiation emitted from the controlled object 15. In a case, however, where the controlled object 15 is used in a vacuum or gaseous atmosphere and hence needs to be isolated from the outside, it is necessary to provide a measuring window in the magnetic suspending device for transmission of infrared radiation emitted from the controlled object 15 or to arrange for the infrared radiation to reach a radiation temperature measuring unit through the interior of the magnetic suspending device via a predetermined path without leaking from the device to the outside. To do this, the magnetic suspending device needs to be specially worked or structured, for example, such that an infrared radiation extraction path using optical fibers is provided, thus causing such a problem as troublesome production process and increase In costs.
Furthermore, in a case where the temperature of the controlled object 15 is measured using any optical technique, if a change in transmittance of infrared radiation due to a smudge on the measuring window or deterioration with age of the optical fibers occurs in a path which transmits the infrared radiation and which runs up to a detection part of the radiation thermometer provided outside the magnetic suspending device, the temperature of the controlled object cannot be measured accurately, and this requires maintenance work including readjustment of the radiation thermometer and replacement of a part of the radiation transmission path.